Printing plate clamp mechanism



0 United States Patent 10,538,850

[72] lnventol' H J- Luehls 2,909,999 10/1959 Polglase et a1 101/278 Westerly, Rhode Island 2,928,342 3/1960 Faeber 1. 101/378 [21] Appl. No. 695,316 2,950,679 8/1960 Krohn et al. 101/378 [22] Filed Dec. 28, 1967 2,953,090 9/1960 Scott... 101/378 continuation-in-part of Ser. No. 428,650, 2,965,024 12/1960 Zi 101/373 Jan. 28, I965, abandoned. 3,019,729 2/1962 Ringe et al. 101/378 [45] Patented Nov. 10,1970 3,195,457 7/1965 Luehrs 101/378 [73] Assignee Harns'ImenyPe Corporation Primary Examiner-Robert E Pulfrey Cleveland, Ohio A on of Ohio smtan! Examiner-.1. Reed Fisher 8 corpora Attorney- Yount, Flynn and Tarolli Disclosed herein d clamp mount- 5 Claims, 12 Drawing Figs mg a printing plate on the cylinder of a rotary pr nting press. The clamp assembly includes springs which resiliently bias a [52] U.S.Cl 101/378 drive assembly to maintain a predetermined clamping force [51] lnLCl B4lf27/l0 against h imin lat during operation of the printing [50] Field ofSearch 101/378, New The drive assembly i selectivfly operated through 8 415-1 passage having a relatively large inlet or mouth which provides access to the drive assembly even when the inlet to the passage [56] References cued is partially blocked by a printing plate. One end portion of the UNITED STATES PATENTS printing plates is advantageously undercut to enable closely 1,012,443 12/1911 Robbins .1 64/7 adjacent printing plates to be removed from the cylinder 2,621,590 12/195 2 Faeber 101/378 without moving clamp members which position the printing 2,893,319 7/1959 Ziebell 101/378 plates on the cylinder.

' Patented Nbv.10,1970 -3,538,850

Sheet of5 Patented Nov. 10, 1970 Sheet 2 of I-NVENTOl. HANS J lUE/l/QS g (5% A 7' TOR/V5 VS Patented NW. 10, 1970 Sheet INVENTOR. HANS cf LUEl/RS Patented Nov. 10, 1970 Sheet INVENTOR. HANS CI LUEHRS BY J ciJM flTTORA/EYS PRINTING PLATE CLAMP MECHANISM This'application is a continuation-in-part of my copending U.S. Pat. application Ser. No. 428,650, filed .Ian. 28, I965, now abandoned, and entitled Printing Plate Gang Lockup Means".

In continuous, high-speed, multicolor printing operations with a rotary press, it is essential that printing plates be firmly secured to a printing cylinder of the press. During operation of the rotary printing press, the plates tend to stretch and work loose from the clamp assemblies commonly used to secure the plates to the cylinder. As the printing plates work loose from clamp assemblies, they move relative to the cylinder and the quality of the' printing is substantially impaired. Therefore, with most known clamping assemblies, it is necessary to periodically stop the operation of the printing press to manually adjust the clamp assemblies to securely retain the printing plates in predetermined positions on the cylinder.

Efficient use of a rotary printing press requires that printing plates, including relatively large printing plates for bleed pages, be mounted in close proximity to adjacent printing plates. However, printing plates are often mounted relatively large distances apart to provide access to a means for manually adjusting the clamp assemblies. Thus, the efficiency of many known rotary printing presses is reduced by the necessity of spacing the printing plates substantial distances apart.

The relatively large distances between ends of adjacent printing plates also results from the necessity of occasionally replacing a printing plate. When replacing a printing plate mounted closely adjacent to other plates on a printing cylinder, interference between an end of the printing plate being removed and an end of a closely adjacent printing plate usually necessitates moving the printing plate being replaced radially outwardly from the cylinder. To move the printing plate radially outwardly from the cylinder, it is usually necessary to completely loosen all the clamp assemblies and to subsequently readjust the clamp assemblies to position a replacement printing plate relative to the cylinder. By mounting the printing plates on the cylinder with the ends of adjacent print ing plates spaced substantial distances apart, it is possible to remove a printing plate by moving the printing plate laterally and radially outwardly from an undisturbed clamp assembly. The undisturbed clamp assembly can subsequently be used to position the replacement printing plate on the cylinder. However, the efficiency of the rotary printing press is impaired by the necessity of mounting the printing plates in a widely spaced-apart relationship to enable any one of the printing plates to be readily replaced.

Accordingly, it is an object of this invention to provide a new and improved means for locating and clamping printing plates on a common printing cylinder in a closely spaced relationship and with a predetermined uniform pressure which is maintained during operation of the printing press.

Another object of this invention is to provide a new and improved printing plate clamp assembly which positively applies and maintains a predetermined clamping pressure on the printing plate during operation of the printing press.

Another object of this invention is to provide a new and improved clamp assembly adjustment means which enables a relatively large printing plate for a bleed page to be mounted closely adjacent to a printing plate for another page.

Another object of this invention is to provide a new and improved means which enables printing plates to be mounted on a cylinder with their ends in close proximity and which enables closely proximate printing plates to be removed from the cylinder while leaving a clamp assembly in position to locate a replacement printing plate relative to the cylinder.

Another object of this invention is to provide a new and improved clamping assembly which has a positive drive means for applying a predetermined clamping force to a printing plate mounted on a cylinder of a rotary press and a resilient means which is compressed after the predetermined clamping force has been applied to the printing plate to maintain the predetermined clamping force on the printing plate during operation ofthe printing press.

Another object of this invention is to provide a new and improved clamping assembly for mounting a printing plate on a cylinder of a rotary printing press, the clamping assembly including helical gears rotatably mounted within the cylinder, a

drive means for rotating the helical gears to apply a predetermined clamping force to the printing plate, and springs which urge the helical gears to move in an axial direction to maintain the clamping force.

Another object of this invention is to provide a new and improved cylinder for a rotary printing press with clamp means extending outwardly from the cylinder and connected to a printing plate having a mounting notch for engaging a clamp.

member extending outwardly from the cylinder of the printing press and an undercut end portion having an end surface which is parallel to a latch surface of the notch so that the printing plate canbe mounted on the cylinder with the undercut end portion in close proximity with an end portion of an adjacent printing plate while still enabling the printing plate to be readily removed from the cylinder.

These and other objects and features of the invention will become more apparent upon a consideration of the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a fragmentary sectional view of a clamp unit including one clamp assembly for engaging the trailing end portion ofa printing plate and another clamp assembly for engaging the leading end portion of an adjacent printing plate;

FIG. 2 is a sectional view, taken along the line 2-2 of FIG. 1, further illustrating the structure of the clamp unit;

FIG. 3 is a fragmentary sectional view, on an enlarged scale, further illustrating the structure of the clamp unit of FIG. 1;

FIG. 4 is a fragmentary sectional view, taken along the line 4-4 of FIG. I, illustrating the structure of a coupling assembly used in the clamp unit;

FIG. 5 is an enlarged plan view of a helical drive gear of the trailing end clamp assembly of FIG. 1;

FIG. 6 is an elevational view, taken along the line 6-6 of FIG. 5, further illustrating the structure of the helical drive gear;

FIG. 7 is an enlarged plan view of a worm wheel used to operate the helical drive gears of the trailing end clamp assembly of FIG. 1;

FIG. 8 is an enlarged elevational view, taken along the line 8-8 of FIG. 7, further illustrating the structure of the worm wheel;

FIG. 9 is a plan view on a reduced scale, of a printing cylinder upon which a plurality of printing plates are mounted with columns and fold lines of the pages around the cylinder and with clamp assembly drive access passage outlets located between end portions of adjacent printing plates;

FIG. 10 is a plan view on a reduced scale, ofa printing cylinder upon which a plurality of printing plates are mounted with columns and fold lines of the pages across the cylinder and 'with clamp assembly access passage outlets located adjacent to side edge portions of adjacent printing plates;

FIG. 11 is a fragmentary sectional view of a clamping unit used with the printing cylinder of FIG. 10; and

FIG. 12 is a fragmentary sectional view, taken along the line 12-12 of FIG. II, illustrating the relative position of end portions of adjacent printing plates on the printing cylinder of FIG. 10.

This invention provides a clamp assembly for mounting a printing plate on a cylinder of a rotary printing press. The clamp assembly includes a plurality of helical drive gears which are mounted within the cylinder and rotatable by a drive assembly to force clamp members into engagement with notches or recesses formed in the bottom of the printing plate. The helical drive gears are movable axially from initial positions to compress springs when uniform, predetermined tension or clamping forces have been applied by the clamp members to the printing plate. The springs then urge the helical gears back to their initial positions to maintain the predetermined forces on the printing plate during operation of the printing press. In one embodiment of the invention, passages having relatively large openings are formed in the cylinder so that an actuator or wrench can be inserted into a passage when the opening is partially blocked by a printing plate. It is another feature of the invention to use printing plates which are undercut at one end to enable any one of the closely adjacent printing plates to be removed from the cylinder while leaving a clamp member undisturbed to subsequently position a replacement printing plate on the printing cylinder.

A clamp or gang lock up unit for engaging leading and trailing end portions 22 and 24 of adjacent printing plates 26 and 28, respectively, is shown in FIGS. 1-3. The clamp unit 20 includes a leading end plate clamp or mounting assembly 39 having clamp members 32 which are slidably mounted in recesses 34 (see FIG. 2) in a cap 36 on a printing cylinder 40 of a rotary printing press. In the illustrated embodiment of the invention, three clamp members 32 engage a leading end mounting notch or undercut 44 in each of the printing plates 26, 28 (the leading end mounting notch 44 and clamp members 33 for only the printing plate 26 being shown in FIG. 3). The clamp members 32 function'to both position the printing plates relative to the printing cylinder 40 and to clamp the printing plates on the cylinder. Similarly, a trailing end plate clamp assembly 46 includes clamp members 48 which are slidably mounted in circumferentially extending recesses 50in the cap 36. The clamp members 48 are movable into clamping engagement with a trailing end mounting notch or undercut 52 formed in the trailing end portion of the printing plate (only the mounting notch 52 for the printing plate 28 is shown). The trailing end clamp assembly 46 applies and maintains a predetermined uniform, tension force against the trailing end portion 24 of the printing plate to thereby hold the printing plate in secure engagement with an associated leading end clamp assembly.

A leading end clamp assembly engages each printing plate to position and hold a leading end portion of the printing plate in a predetermined relationship with the printing cylinder 40. To this end, the leading end clamp assembly 30 (see FIGS. 1- 3) includes axially spaced helical gears 56, 58 and 60 which are rotatably mounted on a shaft 62 located in a recess 70 in the cylinder 40. The recess 70 and shaft 62 extend axially of the printing cylinder 40 to locate the gears 56, 58 and 60 for meshing engagement with gear teeth or racks 64 (FIG. 2) formed on inner or bottom portions of the clamp members 32.

The gears 56, 58 and 60 are interconnected by couplings 66 and 68 having overlapping sets oflugs 70, 72, 74 and 76 which enable the gears 56, 58 and 60 to be readily positioned axially relative to each other. The gears 56, 58 and 60 are positioned on the shaft 62 in a predetermined relationship with their respective clamp members 32 by spacers 78 and washers 80. The gear 58 is fixedly connected to a rotatable shaft 62 by a setscrew 82. The couplings 66 and 68 transmit driving forces from a worm wheel 84, which is integrally formed with the gear 58, to rotate the gears 56, 58 and 60 when a worm gear 86 is rotated. Rotation of the gears 56, 58, 60 moves the clamp members 32 to position the leading end portion 22 of the printing plate 26 relative to the printing cylinder 40.

A detent assembly 94 (FIG. l) is provided for retaining the worm gear 86 and worm wheel 84 against rotation during operation of the printing press so that the clamp members 32 are securely locked against movement relative to the printing cylinder 40. To this end, the detent assembly 94 includes a plunger 96 which is pressed axially by a spring 98 into engagement with teeth 100. The teeth 100 are located radially inwardly of and integrally formed with the worm gear 86. When a positive driving force is applied to the worm gear 86, the plunger 96 is forced out of engagement with the teeth 100 to enable the worm gear to be rotated for small increments to accurately position the leading end clamp members 32.

During operation of the rotary printing press, the printing cylinder 40 is rotated at a relatively high speed and the printing plates mounted on the cylinder are subjected to forces which tend to stretch the printing plates and otherwise work them loose from the clamp assemblies. In order to hold the printing plates against loosening, the trailing end clamp assemblies apply and maintain predetermined tension or clamping forces on the trailing end portions of the printing plates to clamp or pull the leading end portions of the printing plates against the associated leading end clamp assemblies. To this end, the trailing end clamp assembly 46 includes helical drive gears 106, 1108 and M0 (FIG. l) which are mounted on a rotatable shaft 112 in a recess H4 (H6. 3) extending axially of the printing cylinder 40. The helical drive gears M6, M98, meshingly engage corresponding helical teeth or racks R20 (FIGS. 2 and 3) formed on'inner or bottom portions of the clamp members 48. The helical drive gears 106, I08 and 110 are driven through a worm gear 124 which meshingly engages a worm wheel l26 fixedly mounted by a setscrew 12% on the shaft 112. When the worm wheel 126 is rotated by the worm gear 124, drive forces are transmitted to the helical drive gears 106, 108, 110 by coupling assemblies 130, R32, 134 and 136. These drive forces are transmitted to the clamp members 48 to pull the printing plate 26 against an associated leading end clamp assembly (similar to the leading end clamp assembly 30).

In addition to being rotatable with the shaft M2, the helical drive gears W6, I08 and llllt) are slidable axially on the shaft 112. The helical drive gears are resiliently urged in an axial direction to an initial position on the shaft H2 (see FIG. 3) by springs I40, I42, M4 which are mounted coaxially with both the shaft U2 and the helical drive gears. When a printing plate has been pulled against the associated leading end clamp members, the printing plate holds the trailing end clamp members 48 against further circumferential movement relative to the printing cylinder 40. Additional rotational driving force is then applied to the helical drive gears I06, 108 and lit by further rotation of the worm wheel i126. This additional rotational driving force results in the helical drive gears being moved or slid axially along the shaft M2 by a camming action between the teeth of the helical drive gears and the gear teeth on the bottom or inner side of the clamp members 48. This axial movement compresses the springs Mil, 142 and 14 5. The springs then press the helical drive gears axially back toward their initial positions to maintain the predetermined clamping or tension force on the printing plate during operation of the printing press. The springs and helical drive gears are initially positioned relative to each other on the shaft 112 by a spacer 146 secured to the shaft by a setscrew and washers M3, 150.

In view of the foregoing description it can be seen that the helical drive gears 106, E08, 110 are rotated in a counterclockwise direction, as viewed in H6. 3, to move the clamp members 48 into engagement with the mounting notch 52 formed in the trailing end portion of the printing plate 28. As the printing plate is tensioned or pulled against an associated leading end clamp assembly, the clamp members 48 are held by the printing plate and resist further rotation of the helical drive gears 106, 108, 110. The helical drive gears are then forced or cammed in an axial direction by resulting forces between the sloping or angled teeth on the helical drive gears and the similarly sloping or angled teeth on the clamp members 48. This axial force moves or slides the helical drive gear 106 along the shaft 112, in the direction indicated in FIG. 1 by the arrow 15 6, to compress the spring M0. The helical drive gear 108 is urged in the same direction, as indicated in FIG. 1 by the arrow 1%, to compress the spring M2. Since the spring 144 is located to the left (as viewed in FIG. 1) of the helical drive gear lif the teeth of the helical drive gear llli} are sloped or angled in the opposite direction from the teeth of the helical drive gears I06, 108. Therefore, the helical drive gear 110 tends to move or slide along the shaft 112 in the direction indicated by the arrow 158 to compress the spring 144. The compressed springs M0, E42 and 144, then urge the helical drive gears back toward their initial positions to maintain the clamping or tension force on the printing plate during operation of the printing press. Thus, the compressed spring 140 will urge the helical drive gear 106 in the direction of the dashed arrow 159 in FIG. 1. Similarly, the compressed springs 142 and 144 will urge or press the helical drive gears 108 and 110 in the direction of the associated arrows 160 and 161 in FIGQl.

The coupling assemblies 130, 132, 134, and 136 include axially extending lugs which are moved into an increasingly overlapping relationship by the previously described axial movement of the helical drive gears 106, 108 and 110. The structure of the helical drive gear 106 and the coupling assembly 130 is illustrated in greater detail in FIGS. 4, 5 and 6. The helical drive gear 106 includes axially extending lugs 162 which are positioned in an overlapping, abutting relationship with axially extending lugs 164 formed on the spacer 146 (see FIGS. 1, 4 and 5). When the helical drive gear 106 is in the initial position shown in FIG. 1, outer ends 166 (FIG. 5) of the lugs 162 are spaced to the left, as viewed in FIG. 1, from bottom or stop surfaces 168 formed between the lugs 164 on the spacer 146. When the helical drive gear 106 is slid along the shaft 112, in the direction of the arrow 154 to compress the spring 140, the stop surfaces 168 of the spacer 146 are engaged by the ends 166 of the lugs 162 onthe helical drive gear 106 to limit the axial movement of the helical drive gear.

The worm wheel 126 includes axially extending lugs 172 (see FIGS. 7 and 8) which engage axially extending lugs on the helical drive gears 108, 110 in much the same manner in which the axially extending lugs 164 of the spacer 146 engage the lugs 162 on the helical drive gear 106. Since the coupling assemblies 130, 132, 134 and 136 are substantially the same in structure, it will be apparent to those skilled in the art that when the worm wheel 126 is rotated by the worm gear 124, the coupling assemblies transmit drive forces to the helical drive gears 106, 108, 110 while enabling the helical drive gears to move axially along the shaft 112.

The worm gear 124 is driven to rotate the worm wheel 126 by an actuator or wrench 176 (FIG. 3) which is inserted into a tapered passage or bore 180 to engage a connector or socket 182. Rotation of the wrench 176 about its longitudinal axis rotates the worm gear 124 and worm wheel 126 to thereby apply a driving force to the helical drive gears 106, 108 and 110. The rotation of wrench 176 and worm gear 124 is limited by engagement or bottoming out of the lugs of the coupling assemblies 130, 132, 134 and 136 with associated stop surfaces 168. The worm gear 124 is held against rotation during operation of the printing press by a detent assembly 180 (FIG. 2). The detent assembly 180 includes a plunger 182 which engages gear teeth 184 on the worm gear 124 under the urging of the, spring 98 in much the same manner as previously explained in connection with the detent assembly 94.

In the embodiment of the invention illustrated in FIGS. 3 and 9, the printing plates 26 and 28 are mounted on the printing cylinder 40 with columns and fold lines of the pages around the cylinder. The printing plates are located on the cylinder with side or lateral edges 200 and 202 (FIG. 9) of adjacent printing plates in close proximity to allow for bleeds or maximum printing area in this direction. A relatively large outer opening is located between the trailing end portion 24 of the printing plates 28 and the leading end portion 22 of the printing plates 26. A similar tapered access passage, having an inlet opening or mouth 208, is provided for the leading end clamping assembly 30. The opening or mouth 208 is also located between adjacent end portions of the printing plates 26 and 28. These relatively wide mouths or inlet openings enable the relatively small stern of the actuator wrench 176 to be inserted into the tapered passages when the opening or mouth is partially blocked by a printing plate, as illustrated in FIG. 3.

If a longitudinal bleed page is to be printed by one of the printing plates 28, the printing plate will have a relatively large longitudinal or circumferentially extending dimension. The relatively long bleed page printing plate 28 will partially block the inlet 206 to the passage 180. However, the relatively large size of the inlet 206 enables the actuator wrench 176, which has a small transverse dimension, to be tilted and inserted into the tapered passage 180 to engage a socket or connector 182 to thereby rotate the worm gear 124 (see FIG. 3). Of course, if a bleed page was to be printed by one of the printing plates 26 and a normal size page was to be printed by the adjacent printing plate 28, the actuator wrench 176 would merely be shifted or tilted to the right of the position shown in FIG. 3. The passages for access to the worm gear of the leading end clamp assembly cooperate with the actuator wrench 176 in much the same manner as explained for the passages 180.

It is often desirable to mount the printing plates on the printing cylinder with columns and fold lines of the pages across the cylinder. With this arrangement the printing plates are advantageously located on the cylinder with the end portions of the printing plates in close proximity to provide narrow end margins for bleeds or maximum printing area. Such a mounting arrangement is shown in FIGS. 10 and 12 for printing plates 220 and 222 on a printing cylinder 224 of a rotary printing press. When the printing plates are mounted as shown in FIG. 10, access passages 228 for leading end clamp assemblies 230 (FIG. 11)-are located between the circumferentially extending edges 232 of the printing plates. Similarly, access passages 234 for'trailing end clamp assemblies 236 (FIG. 11) are located between the edges 232 of the printing plates adjacent to thetrailing end of the printing plates. Of course, the access passages 228 and 234 can be tapered as previously explained in connection with the embodiment of the invention shown in FIGS. 1-9 to provide access to the clamp assemblies when relatively large page printing plates are mounted closely adjacent to other printing plates.

A leading end clamp assembly 230 of the printing cylinder 224 is illustrated in FIG. 11 and includes an integrally formed gear shaft 240 which is mounted in and extends axially of the printing cylinder 224. Axially and radially extending straight spur gear teeth 242 are formed on the gear shaft 240 for engagement with gear teeth formed on leading end clamp member 32 of FIGS. 2 and 3. The gear shaft 240 is rotated by a worm 244 which engages a worm wheel 246 formed on the shaft. The integrally formed gears 242 and worm wheel 246 of the leading end clamp assembly eliminate the necessity of forming and assembling a plurality of separate gears. Of course, the leading end clamp assembly of the embodiment of FIGS. 1- -9 could be constructed in the same manner as in which the leading end clamp assembly 230 is constructed.

The trailing end clamp assembly 236 of the printing cylinder 224 is generally similar in structure to the trailing end clamp assembly 46 of the embodiment of FIGS. 1-9. Thus, the trailing end clamp assembly 236 includes a plurality of helical drive gears 252, 254 and 256 which are rotatable and slidably mounted on a shaft 258. Drive forces are transmitted to the helical drive gears 252, 254, and 256 by a worm 260 and a worm wheel 262 through couplings 266, 268 and 270 which are constructed in much the same manner as are the couplings 130, 132, 134 and 136 of the embodiment illustrated in FIGS. 1-9. It should be noted that a plurality of setscrews 274 are provided so that the helical drive gears 252, 254 and 256 are rotated by the couplings with the shaft 258. The helical drive gears are rotated to apply uniform tension or clamping forces to clamp members which engage the trailing end portion of the printing plates. These uniform tension or clamping forces are maintained during operation of the rotary printing press by springs 278 which are compressed by axial movement of the helical drivegears along the shaft 258 after a predetermined tension or clamping force has been applied to the printing plates, in the manner previously explained in connection with the embodiment of FIGS. 1-9. this clamping force is maintained by the springs 278 during operation of the rotary printing press.

It should be noted that for both the embodiment of FIG. 9 and the embodiment of FIG. 10, the actuator wrench 176 is inserted through openings which are located adjacent to the printing plates to enable a single operator to both hold and lock the printing plates. Thus, the access openings 206 and 208 for the embodiment of HO. 9 are located adjacent to the leading and trailing ends of associated printing plates. The access openings 228 and 234 for the embodiment of H0. 10 are similarly located, but are adjacent to side edges 232 of the printing plates.

After the rotary printing press has been in operation for a period of time, it is occasionally necessary to replace one of the printing plates. However, each of the printing plates is located in a predetermined circumferential position on the printing cylinder 224 by associated leading end clamp metnbers 284 (H0. 12). A replacement printing plate must be located in the same position on the printing cylinder 224 as was the printing plate which it replaces. To facilitate locating a replacement printing plate on the cylinder, it is desirable to be able to remove a printing plate from the cylinder without loosening or disturbing the position of the clamp members 284 for the leading end portion of the printing plate. The leading end portion of a printing plate is clamped on the printing cylinder 224 by engagement of an undercut latch tooth 286 with a latch or clamp surface 290 of a mounting notch or scarf 292 formed in the printing plate. The latch or clamp surface 290 extends outwardly at an acute angle from an inner surface 294 of the printing plate 220. The latch surface 290 also slopes forwardly at an angle to a radius of the printing cylinder 224 to engage the undercut forward surface of the latch tooth 286.

In order to remove the printing plate 22% from the printing cylinder 224 without disturbing or releasing the leading end clamp assembly 230, it is necessary to release the trailing end clamp assembly 236 and move the printing plate 220 outwardly from the printing cylinder 224 along a path extending generally parallel to the latch surface 290 so that the forwardly projecting outer end of the undercut latch tooth 286 is cleared by the latch surface. To allow for this movement, the leading end of the printing plate 220 is undercut, that is the forwardmost surface 298 extends rearwardly from an operating or ink carrying surface 300 of the printing plate 220 to the inner surface 294 and is generally parallel to the latch surface 290. This parallel relationship between the latch surface 290 and forward end surface 298 enables the printing plate 229 to be removed from the printing cylinder 224 without disturbing or releasing the leading end clamp assembly when the leading end of the printing plate is mounted in close proximity to the trailing end of an adjacent printing plate, as shown in H6. 12. The undercut forward or lead end of the printing plate will clear a rearward or trailing corner 362 of the closely adjacent printing plate 222 when the printing plate 220 is moved outwardly from the printing cylinder 224 on a path extending parallel to the surfaces 290 and 29%. If the forward surface 298 of the printing plate 220 extended in a generally perpen dicular relationship with the operating or ink carrying surface 300 of the printing plate, the inner leading corner of the printing plate 220 would interfere with or engage the outer trailing corner 302 ofthe printing plate 222 as the printing plate 220 is moved outwardly from the printing cylinder 224- on a path parallel to the latch surface 294).

in view of the preceding description, it can be seen that a leading end clamp assembly 30 is provided for positioning and clamping a printing plate on the printing cylinder 40. A predetermined tension or clamping force is provided by the trailing end clamp assembly for securely holding the printing plates on the printing cylinder during operation of the printing press. This predetermined clamping force or tension is maintained on the printing plate due to the action of the springs 140, M2 and M4 in pressing or urging the helical drive gears 106, 108 and lit) axially back toward their initial positions. Since the tension or clamping force is maintained during operation of the printing press, the operation of the printing press does not have to be stopped to periodically tighten the clamp assemblies.

The clanip assemblies are advantageously provided with tapered access passages to enable an actuator or wrench to be inserted into the passage when the passage is partially blocked by a relatively large printing plate, such as is commonly used when printing bleed pages. In the embodiment of the invention illustrated in FIGS. E li-l2, the printing plates have undercut leading end portions which enable the printing plates to be removed from the printing cylinder without releasing or disturbing the leading end clamp assemblies even though the printing plates are mounted with adjacent leading and trailing ends in close proximity.

it is anticipated that many changes will be made by those skilled in the art to the illustrated embodiments of the invention. For example, the clamp assemblies could be operated or actuated through passages extending axially of the printing cylinder. The clamp assemblies could also be coupled together to position a plurality of similar printing plates on the printing cylinder. It is also contemplated that the specific clamp as sembly structure could be modified by using couplings other than the ones shown to interconnect any desired number of helical drive gears while enabling the helical drive gears to move axially relative to the printing cylinder.

I claim:

1. A clamp assembly for securing a printing plate to a rotary cylinder of a printing press, said clamp assembly comprising a plurality of members for engaging the printing plate, said members having a plurality of inwardly projecting teeth disposed at an acute angle to a longitudinal axis of the cylinder, a shaft rotatably mounted within the cylinder and extending generally parallel to the longitudinal axis of the cylinder, drive means connected to said shaft for rotating said shaft relative to the cylinder, a plurality of helical gears slidably mounted on said shaft and movable axially along an outer surface of said shaft, said helical gears having teeth disposed at an acute angle to the longitudinal axis of said shaft and in meshing engagement with said teeth on said members, coupling means operatively interconnecting said shaft and said gears for transmitting driving forces thcrebetween upon rotation of said shaft under the influence of said drive means, said coupling means including a plurality of axially projecting lugs connected to said shaft and a plurality of axially projecting lugs on end portions of said helical gears, said lugs on said helical gears extending intermediate said lugs fixedly secured to said shaft whereby said gears are rotated upon rotation of said shaft to thereby move said members into engagement with the printing plate, said lugs on said helical gears having sufficient axial extent to enable said gears to slide axially along said shaft from first positions to second positions while extending intermediate said lugs connected to said shaft, and spring means for resiliently urging said helical gears toward their first positions, said helical gears being movable to their second positions against the influence of said spring means by an interaction between the teeth on said members and the teeth on said helical gears when predetermined clamping forces are applied to the printing plate by said members, said helical gears being urged toward their first positions by said spring means to maintain the predetermined clamping forces during operation of the printing press.

2. A clamp assembly as set forth in claim 3 wherein said spring means is coaxial with said shaft and is located between said shaft and said lugs.

3. A clamp assembly as set forth in claim 3 wherein said drive means includes a worm wheel mounted on said shaft and connected in a driving relationship with said helical gears by said couplings means, and a worm gear mounted in meshing engagement with said worm wheel, said cylinder having an opening in its outer surface providing access to said worm gear to enable said worm gear to be rotated to thereby operate said clamp assembly.

4. A rotary printing cylinder as set forth in claim 3 where in said worm gear is adapted to be drivingly engaged by an actuator and said opening is relatively large compared to a transverse cross section of said actuator to enable said actuator to be inserted through said opening into driving engagement with said worm gear when said opening is partially blocked by a printing plate.

5. A rotary printing press cylinder as set forth in claim 3 wherein a tapering bore is formed in said worm gear, said bore having a relatively large outer end in communication with said 

